1. Field of the Invention
The present invention relates to an ink jet ink having good color developability, good humidity resistance, and high reliability as ink jet ink; an ink jet recording method; a recording unit; an ink cartridge; and an ink jet recording apparatus.
2. Related Background Art
An ink jet recording method is a recording method involving applying a small ink droplet to any one of recording media such as plain paper and glossy media to form an image, and has become rapidly widespread owing to a reduction in its cost and an improvement in its recording rate. With the rapid spread of a digital camera in addition to an improvement in quality of an image recorded by the method, the method has been generally used as a method of outputting a photographic image comparable to silver halide photograph.
In recent years, image quality has undergone improvement more than ever owing to, for example, extreme reduction in size of an ink droplet and an improvement of the color gamut involved in the introduction of multi-color ink. Meanwhile, there have been growing demands for a coloring material and ink, and stricter properties have been required in terms of an improvement of color developability and reliability such as sticking property or ejection stability.
As compared to silver halide photography, the ink jet recording method is problematic in terms of, for example, the image storage stability of the resultant recorded article. In general, the recorded article obtained by means of the ink jet recording method is inferior in image storage stability to a silver halide photograph, and involves a problem in that a coloring material on the recorded article is apt to deteriorate to cause a change in color tone of an image and color fading of the image when the recorded article is exposed to light, humidity, heat, an environmental gas present in the air, or the like for a long period of time. To solve the problem, a large number of proposals have been conventionally made.
In general, the ink jet recording method involves the use of inks each having a hue of yellow, magenta, cyan, black, or the like. It has been heretofore acknowledged that the yellow ink out of the inks must be improved in light resistance, water resistance, humidity resistance, and the like. For improving these properties, there has been proposed, for example, the use of a coloring material having a specific structure such as C.I. Direct Yellow 173 or C.I. Direct Yellow 86 (see, for example, Japanese Patent Application Laid-open No. H02-233781 and Japanese Patent Application Laid-open No. H04-233975). The use of such coloring material as mentioned above shows significant improvements in light resistance, water resistance, and humidity resistance, but color tone, color developability, reliability, and the like are not at sufficient levels.
There has also been proposed the use of C.I. Direct Yellow 132 as any one of a yellow ink and a coloring material for an ink set (see, for example, Japanese Patent Application Laid-open No. H11-29729 and Japanese Patent Application Laid-open No. 2001-288391). Although the coloring material has often been used for ink jet ink because of its good color developability, the coloring material involves a problem in that its humidity resistance is remarkably bad.
There have also been proposed the use of a coloring material having a specific structure to aim at improving humidity resistance (see, for example, Japanese Patent Application No. H11-217529) and the use of an ink set of multiple colors to improve humidity resistance (see, for example, Japanese Patent Application Laid-open No. H11-180028).
Each of the proposals described above has attempted to improve humidity resistance, but merely depends on the structure of a coloring material. In other words, neither the proposal for improving humidity resistance by means of a coloring material having a specific structure nor the proposal for improving humidity resistance by means of an ink set of multiple colors can prevent migration (image deterioration due to a change in color tone in an environment such as a high-temperature-and-high-humidity environment).
There has also been proposed the synthesis of a novel coloring material having humidity resistance, light resistance, water resistance, and a hue and sharpness suitable for ink jet recording (see, for example, Japanese Patent Application Laid-open No. 2003-321627). However, even when such coloring material is used, a certain ink prescription cannot reach the level of humidity resistance requested in a current ink jet recording method in some cases.